Conventionally, a plasma etching apparatus using a radial line slot antenna is known (see, e.g., Japanese Patent Application Publication No. 2007-311668). In this plasma etching apparatus, a circular plate-shaped slot antenna having a plurality of slots is installed on a dielectric window of a processing chamber. The slots include a plurality of slot pairs formed of two elongated microwave radiation slots directed in different directions. The slot pairs are arranged in a double ring shape (i.e., a concentric circular shape) about the centroid position of the slot antenna. The microwave is incident on the central position of the slot antenna, emitted radially, and radiated from the slots. The microwave radiated from the slots of the slot antenna is introduced into a processing space of the processing chamber through a dielectric window made of a dielectric material. A processing gas is turned into a plasma by the energy of the microwave.
The microwave plasma generated by the radial line slot antenna has a feature that a plasma having a relatively high electron temperature of several eV which is generated just below the dielectric window (referred to as “plasma excitation region”) is diffused and becomes a plasma having a relatively low electron temperature of about 1 eV to 2 eV in a region just above a substrate and below the dielectric window by a distance of about 100 mm or more (referred to as “plasma diffusion region”). In other words, the electron temperature distribution of the plasma occurs as a function of a distance from the dielectric window.
In the radial line slot antenna type plasma etching apparatus, an etching gas is supplied to a low electron temperature region and dissociation control of the etching gas (control of the amount of etching species generated in the plasma) is performed. By doing so, etching reaction (chemical reaction on a substrate surface by the etching species) is controlled. Accordingly, the etching can be performed with high precision and damage to the substrate is considerably reduced. For example, when etching or the like is performed in a step of forming a spacer, it is possible to manufacture devices with design dimensions and reduce the damage to the substrate such as a recess or the like.
However, as the processes become various and complicated, the plasma stability needs to be further improved. For example, in the plasma etching apparatus using a radial line slot antenna described in Japanese Patent Application Publication No. 2007-311668, the radiation electric field intensity is decreased in the case of using as a processing gas a negative gas that is turned into negative ions due to attachment of electrons in the plasma diffusion region. Therefore, in order to ensure the plasma stability, it is required to control a pressure or a microwave power.